I'm never said BSNL provides 100% service to all 100% customers. Errors happen everywhere with everyservice provider and not just confined to BSNL.
Even I've had billing issues with them which got sorted by taking things through the right track. If there is an issue, then anyone needs to take it up with them rather than do little and do nothing and just complain and assume that someone should get a brain pulse that you have billing issues and sort it out automatically. No offence mate, but problems are not just confined to a single ISP.
There wouldn't be a need to change of modem as all the modems that BSNL supplied supports annexure b which is 8Mbps